1. Field of the Invention
The present invention relates in general to a backlight device, wherein it is easy to replace the tubular lamps of the backlight device.
2. Description of the Related Art
Backlight devices are widely used in liquid crystal displays (LCDs) and scanners. A backlight device has tubular lamps inside to generate light. The lamps need to be replaced when they burn out. U.S. Pat. No. 5,537,296 discloses a structure of a backlight device, the only one part that the backlight device of the burned liquid crystal displays need to replaced is the tubular lamp. Other elements besides the burned lamp are left without being replaced together. However, it is difficult for an operator to disassemble and assemble the backlight device for repairing the burned lamp. JP patent No. 4-104486 and 4-288526 simplify the structure of the backlight device for easy maintenance, wherein the burned lamp is drawn out from the side surface of the backlight device. However, when the friction applied to the lamp is great, it is difficult to draw out a tight tubular lamp.
FIG. 1A is an exploded perspective diagram of a conventional backlight device, wherein the directions of top, bottom, left, right, front and rear are defined for easy description. The backlight device includes a first frame 1, a diffuser 2, a lighting guide 3, a reflection sheet 4, a second frame 5, a back plate 6 and two lamp assemblies 7. In the assembling operation, the back plate 6 and the second frame 5 are screwed together via screws 61, and it looks like a box without a cover. Then, the reflection sheet 4, lighting guide 3 and diffuser 2 are put in the box in sequence, with one laid over another. Grooves 51 are formed between the second frame 5 and the lighting guide 3. The lamp assemblies 7 are inserted, from the right to the left, into the grooves 51. Then, the second frame 5 is engaged with the first frame 1 by the engaging portions 52 to fix all of the elements 4, 3, 2, 7 therebetween.
Referring to FIG. 1B and FIG. 2, each lamp assembly 7 includes two fluorescent tubes 72, a tube guard 71 covering the fluorescent tubes 72, and a base 73 for fixing the fluorescent tubes 72 in the tube guard 71. Light is emitted from the fluorescent tubes 72 to propagate in the lighting guide 3 in two paths: (1) Light 75 passes through the front surface of the lighting guide 3 and then propagates out from the diffuser 2. (2) Light 76 passes through the rear surface of the lighting guide 3, is scattered by protrusions 31 on the lighting guide 3, is reflected by the reflection sheet 4 back to the lighting guide 3, and then propagates out from the diffuser 2. The protrusions 31 on the rear surface of the lighting guide 3 are used for scattering the light 76. The diffuser 2 is provided to further scatter the light 76 so that the distribution of the light 76 out from the diffuser 2 is more uniform (without the diffuser 2, the images of the protrusions 31 can still be observed by the user in front of the lighting guide 3).
It is important that the distance between the fluorescent tubes 72 and the lighting guide 3 must be accurately kept, otherwise (a) the light emitted out from the upper portion and lower portion of the lighting guide 3 will be too strong due to the fluorescent tubes 72 are too close to the lighting guide 3. (b)On the other hand, the light emitted out from the upper portion and lower portion of the lighting guide 3 will be poor due to the fluorescent tubes 72 are far away from the lighting guide 3.
FIG. 3 is a front view of FIG. 1A, wherein the lighting guide 3, the reflection sheet 4, the second frame 5 and the back plate 6 are already assembled. Also, the diffuser 2 and the first frame 1 are not shown in FIG. 3. In assembling operation, the lamp assemblies 7 are inserted into grooves 51 from the right to the left, wherein the grooves 51 is formed and disposed between the second frame 5 and the lighting guide 3. In the disassembling operation, ordinary the lamp assemblies 7 are pulled out from the grooves 51 from the left to the right. The widths of the grooves 51 and those of the lamp assemblies 7 are well matched to keep the lamp assemblies 7 tight, therefore, it is difficult for an operator to assemble/disassemble the backlight device due to a great friction between the lamp assemblies 7 and the grooves 51.
An object of the present invention is to provide a backlight device with easy maintained tubular lamps.
The backlight device of the present invention includes a frame, alighting guide and at least one lamp assembly. The frame has an inner surface. The lighting guide is disposed inside the frame. The lamp assembly is disposed inside the frame and beside the lighting guide. A gap is provided between the inner surface of the frame and the lamp assembly to decrease the friction between the lamp assembly and the frame, thereby facilitating the replacement of the tubular lamp.